1. Field of the Invention
The present invention relates to electrical cable connections and more particularly to electromagnetic interference (EMI) shielding for cable connectors.
2. Prior Art
In the prior art, various means have been employed to prevent unwanted electromagnetic energy from entering machine cabinets through external electric cables. In the past, jacketed cables with braided shielding have been stripped back from the connector end and the shield terminated to the frame.
The following are examples of prior art patents which describe various mechanisms for attaching an electrical cable shield to a frame to reduce electromagnetic interference. However, it should be noted that none of the prior art patents below teach or suggest the external cable grommet according to the present invention.
U.S. Pat. No. 5,012,042 shows a shielded cable entry device having two body members and a securing nut each of the body members including a semihexagonal flange, semicylindrical shells for making contact with the cable shielding and receiving compressing springs in the threaded section. The device of the patent is relatively complex and requires several more parts than does the simple solution of the present invention.
Japanese Patent 2,082,695 is an example of the prior art discussed above wherein the shield braid is brought back and attached to the frame as a braid strap.
U.S. Pat. No. 4,577,054 shows a coaxial feedthrough consisting of a feedthrough body having a rectangular flange with a threaded coupling through which a coaxial cable is inserted and soldered. On the flange side, the cable is terminated in such a manner that the outer jacket and the dielectric material of the cable are flush with the flange. The cable center conductor protrudes a short distance beyond the flange for the purpose of connecting a ribbon or wire circuit element.
The patent does not teach or suggest the simple but effective device according to the present invention.
U.S. Pat. No. 4,557,545 shows a shielded electrical connector in which the shield cover is formed as two U shaped parts each of which includes an integral clamping portion for clamping with a shielded connector. The clamping portions are connected to the cover parts by leg portions. The clamp portions are clamped about the cable to provide electrical connection between the cable and the shield cover.
The connector of the patent does not suggest the present invention which provides for a completely encircled fully shielded connection as close to the frame as possible.
U.S. Pat. No. 4,468,080 teaches a cable termination means having a metal plate which fits into the open cable receiving end of a connector plug or receptacle, the plate having a number of openings into which one or more hollow metal tubes are received and conductively secured to the plate. One or more insulated cable wires are located within a ground shield, an end portion of which is peeled back preliminarily and connected to an appropriate connector contact. A ring of solder may be used to affix the shield and tube together both mechanically and electrically. Optionally, an aluminum ring may be clamped over the shield by a so-called cryo ring through which an electric current is passed and a further shield connection technique is to employ an oversize ferrule crimped by the use of a suitable tool down on the shield. The mechanism of this patent is much more complex and time consuming to install than is the simple grommet according to the present invention.
U.S. Pat. No. 4,464,540 shows a shield connection device for connecting EMI shielded cable shield to an EMI enclosure, the device including an electrically conductive body defining a shield termination enclosure, the body having a number of openings extending through the body, the openings substantially parallel to the longitudinal axis of the body and the body having means for accessing the opening. A connection device includes means adjacent to the access means for applying electrically conductive material to the opening through the access means for electrically connecting the EMI cable shield thereto.
The mechanism of the shield termination enclosure of the patent is much more complex and time consuming to install than the grommet according to the present invention.
U.S. Pat. No. 4,433,206 shows an EMI shielded connector assembly in which the shield is formed into a pigtail and secured to the shell of the connector assembly, similar to the ground shield braid strap discussed above.
None of the prior art devices described shows a simple low cost solution to the problems of connecting cable shields to a frame for the purpose of reducing electromagnetic interference from flowing into an EMI shielded enclosure.